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A series of cerium samarium tungstates Ce(2– x )Sm x (WO4)3 with $x \le 0.3$ was synthesized by a coprecipitation method followed by thermal treatment at 1000 °C. The polycrystalline compounds were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) experiments. Using the Rietveld procedure, the decrease in cell parameters showed that a solid solution was obtained. A comparative analysis of diffraction profiles allowed determining structural distortions increasing with increasing composition $x$ . The PL experiments were performed under UV and XR excitations. The variations with composition $x$ of emission intensities observed in the wavelength range of 500–1000 nm, corresponding to complex charge transfers (CTs) and quenching effects, were interpreted in terms of transitions proper to Ce3+ and Sm3+ cations, accompanied by additional transitions due to oxygen vacancies and other point defects due to substitution and synthesis conditions.

International audience; Having clear and deep information on the surface/interface of deposited molecules is of crucial importance for the development of efficient optoelectronic devices. This paper reports on a joint experimental/theoretical approach based on Raman spectroscopy in order to provide information on the orientation of deposited push-pull chromophores onto a gold surface. In addition, several parameters can strongly control or impede the orientation of such molecules on the surface such as: the molecular structure, the surface itself, the method of deposition and the solvents used. From this approach, additional information has been highlighted such as perpendicularly depositing the molecule on the surface, the bithiophene compounds displaying more solvent effects compared to terthiophene molecules and so on. According to the results, the joint SERS/DFT study proves to be an effective tool for probing the arrangement of push-pull chromophores and selecting right experimental conditions to tune the surface properties.

A series of polycrystalline barium-lead tungstate Ba1-xPbxWO 4 with 0 ≤ x ≤ 1 was synthesized using a classical solid-state method with thermal treatment at 1000 °C. These materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Raman (FT-Raman) spectroscopy. X-ray diffraction profile analyses were performed using Rietveld method. These materials crystallized in the scheelite tetragonal structure and behaved as quasi ideal solid solution. Raman spectroscopy confirmed the formation of the solid solution. Structural distortions were evidenced in X-ray diffraction profiles and in vibration Raman spectra. The scanning electron microscopy experiments showed large and rounded irregular grains. Luminescence experiments were performed under X-ray excitation. The luminescence emission profiles have been interpreted in terms of four Gaussian components, with a major contribution of blue emission. The integrated intensity of luminescence reached a maximum value in the composition range x = 0.3–0.6, in relation with distortions of crystal lattice.

In this paper, strontium lead molybdate Sr1-xPbxMoO4 polycrystalline samples with 0

International audience; Two series of A-site and B-site Eu3+ doped (SrxBa1-x)(2)CaWyMo1-yO6 double perovskite phosphor materials were prepared via a modified Pechini sol-gel route; (SrxBa1-x)(1.96)Eu(0.02)K(0.02)CaW(y)Mo(1-)yO(6) and (SrxBa1-x)(2)Ca0.96Eu0.02Li0.02WyMo1-yO6 (x and y=0, 0.25, 0.50, 0.75, 1). The Sr/Ba ratio was the main determinant for the crystal symmetry of the series, while variation in the W/Mo ratio did influence the crystal symmetry significantly. The crystal structure evolved with Sr/Ba ratio from cubic Frn (3) over barm for x=0, via tetragonal 14/m for x=0.25, to monoclinic P2(1)/n for x >= 0.5, as verified by Rietveld refinement of X-ray diffractograms as well as by Raman spectroscopy. The reported boundaries for the compositionally induced phase transitions are in very good agreement with reported optical properties. (C) 2015 Elsevier Inc. All rights reserved.

We compare the Raman scattering properties of hybrid nanostructures consisting of Ag nanoparticles (NPs) in disordered and aligned arrangements on single-walled carbon nanotubes (SWCNTs) as a result of chemical and photoreduction methods. In the latter case, the unique structure of the very small Ag NP (from 4 to 7 nm) chains generated an extremely large mode at 969 cm(-1) that was assigned to the sulphate-silver interaction at the NP surface. Another strong mode was present at 1201 cm(-1) and was assigned to an IR-active mode of sodium dodecyl sulphate (SDS); this mode was observed because the symmetry changes altered the selection rules. We demonstrate that both the UV photoreduction of silver and the presence of SWCNTs are necessary to produce this very strong Raman scattering. The Raman modes of the SWCNTs are also significantly modified by the presence of Ag NP chains along the nanotubes.

International audience; A singular adaptive phenotype of a parthenogenetic insect species (Acyrthosiphon pisum) was selected in cold conditions and is characterized by a remarkable apparition of a greenish colour. The aphid pigments involve carotenoid genes well defined in chloroplasts and cyanobacteria and amazingly present in the aphid genome, likely by lateral transfer during evolution. The abundant carotenoid synthesis in aphids suggests strongly that a major and unknown physiological role is related to these compounds beyond their canonical anti-oxidant properties. We report here that the capture of light energy in living aphids results in the photo induced electron transfer from excited chromophores to acceptor molecules. The redox potentials of molecules involved in this process would be compatible with the reduction of the NAD+ coenzyme. This appears as an archaic photosynthetic system consisting of photo-emitted electrons that are in fine funnelled into the mitochondrial reducing power in order to synthesize ATP molecules.

Copper oxalate (CuOx) mesocrystalline nanostructures have been synthesized by aqueous precipitation. Several morphologies of these nanostructures could be obtained with high monodispersity dependin...

Aggregates of Au nanoparticles have been extremely easily obtained on glass substrates by physical sputtering under primary vacuum. With such a protocol, we demonstrate that it is possible to control the surface plasmon band absorption. Surface enhanced Raman spectroscopy (SERS) experiments were performed with methylene blue, zinc octacarboxyphthalocyanine, 4-aminothiophenol and cysteamine. The correlation between the absorption band and the wavelength giving the highest SERS intensity is clearly observed for methylene blue, in accordance with the electromagnetic enhancement theory. For the other molecules, effects of the chemical enhancement are also observed. In addition, we noticed a strong influence of the nature of the adsorbed molecule on the enhancement factor for a given wavelength. The origin of this feature is discussed in terms of resonant effects or multipolar surface plasmon modes.

Copper oxalate has been precipitated in water and acetone. Raman spectroscopy is performed to validate the chemical composition of the obtained powders. Aqueous precipitation has led to micrometer-scaled agglomerates, whereas acetone precipitation has led to nanorods showing a two-dimensional (2D) self-organization when deposited on a Si substrate. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) show an anisotropic structure of the agglomerates with two kinds of faces. Nanoplatelets with self-assembly abilities are also detected in the copper oxalate aqueous suspension. These observations reveal a supracrystalline self-assembly process leading to micrometer-scaled three-dimensional (3D) superstructures. AFM measurements on nanoplatelets and nanorods are correlated to X-ray diffraction results. A kinetic study carried out by SEM highlights four main steps in the 3D self-assembly process. Each step corresponds to a specific assembly speed ratio between the two directions that define the...

1 - Article; Tip-enhanced Raman spectroscopy has proven to be a promising technique for stress/strain mapping of silicon-based semiconductor devices on the nanometer scale. Field enhancement factors of up to 104 have been reported and a spatial resolution down to 20 nm has been claimed through exploiting far-field suppression techniques based on an appropriate choice of the excitation/detection polarization states. In this paper, we show that depolarization of light due to scattering from the tip plays a key role in the selective enhancement of the one-phonon optical mode peak at 520 cm−1 with respect to the two-phonon ones. The spatial confinement of the selective enhancement has been studied by means of approach curves, and its dependence on the excitation wavelength and power further explored. Conclusions on the physical nature of the enhancement (depolarization- or plasmonic-based) are presented. Copyright © 2009 John Wiley & Sons, Ltd.